The authoritative public forum
  for Metal Finishing since 1989
-----

Science question about copper sulphate

Why do we see the solution of copper sulphate ⇦this on eBay or Amazon [affil links] blue? Is it because of reflection or transmission?

Michael [surname deleted for privacy by Editor]
- India
2002

---

I recall seeing in a museum once a feather from a blue bird mounted on the wall of a display case with a light mounted behind the case and a small hole cut in the case behind the feather. When the feather was viewed in this transmitted light it was white, proving that there was no blue dye in the feather; rather, the blue color was a matter of refraction.

I suggest you position a strong light behind a beaker [beakers on eBay or Amazon [affil links] of copper sulphate in a darkened room, look through the beaker toward the light, and report what you find. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

---

SOLUTIONS ABSORB LIGHT FROM SUNLIGHT (ALL COLORS) AND THE COLOR YOU SEE IS THE LIGHT NOT ABSORBED BY YOUR SOLUTION. SO copper sulphate ABSORBS ALL COLORS (WAVELENGTH) OF SUNLIGHT EXCEPT BLUE. BLUE COLOR INCLUDE WAVELENGTH FROM ABOUT 450 TO 500 nm.

If you look your solution using red light you will see a black solution because all that light was absorbed.

HECTOR LONGUEIRA BOJANOVIC
- ANTOFAGASTA, CHILE
2005